The present invention relates to a tensioning device for belts, in particular toothed belts for transmitting motion from the crankshaft to the camshaft of an internal-combustion engine.
It is known that a tensioning device is intended to ensure a substantially constant tension of a belt as the thermal and wear conditions vary. For this purpose, such a device comprises a pulley mounted to rotate eccentrically about a mounting pivot and loaded elastically in the direction of the belt.
Currently a mounting pivot for a pulley is made from steel and is fitted into a support plate which, in turn, is secured to a fixed wall (for example, to a wall of an engine block). This solution not only necessitates substantial outlay on the mounting of the pivot but also has the disadvantage of not always ensuring perfect perpendicularity of the pivot with respect to the associated support plate. This lack of perpendicularity has a particularly detrimental effect if the tensioner pivot is disposed projecting from the support plate, or if the support plate is secured to the respective fixed wall in a position which is not coaxial with respect to the pivot. In fact, in this case the error at the pivot is amplified by possible geometrical imperfections in the support plate caused by the high lever arm prevailing between the fastening point of the plate and the pivot. Consequently, the pivot assumes an effective position which is displaced to a not inconsiderable extent with respect to the nominal position and generates nonuniform forces along the section of the belt, as a result of which the belt, which is not retained transversely, can slip with respect to the pulley and lose contact therewith.